In the United States, Psychiatric Emergency Services facilities are a type of acute psychiatric facility that is available for mental health emergencies. They are generally open 24 hours a day in the United States, although most well developed countries will have one in some form or another. Mental health provision for the indigent in the United States is divided by counties, after the passage of a federal Community Mental Health Law in 1963.

Most large counties have established a PES, or similarly named facility to handle emergency cases. The staff of an emergency psychiatry unit may consist of psychiatrists (MD), registered nurses (RN), psychologists (PhD), social workers (CSW), psychiatric technicians (like a hospital orderly), clerical staff and security officers. These units are often how the most severely ill patients will begin to get the help they need from the Medical System. PES helps coordinate care for the most severely ill in a county. PES clinics are specific places for patients to be referred to for emergency care. A PES clinic may be located within a general medical hospital, within a psychiatric hosptial, or as a free-standing clinc in its own right.

Patients may arrive in several ways: they could be taken in by the police, for instance after an offence has been committed, sent from other emergency rooms, sent from outpatient clinics, referred from physician's offices, brought in by family or friends or voluntary presentation by the individual. PES clinics are often locked due to the possibly violent nature of the patients. Not all patients are involuntary in PES clincs, but may are. Often the person is too ill to know they are ill and must be brought in by othes. Mental health laws vary from state to state and country to country, but people can generally only be held against their will (involuntary commitment) for being a danger to themselves, danger to others or the inability to provide food, clothing and shelter for themselves. In the past 30 years mental health laws have become much stricter meaning that persons can only be involuntary committed if they meet the above criteria. Simply having a mental illness is almost never grounds for detaining someone.

In the past, chronically ill patients were committed to state hospitals, often for years. In the 1970s-1980s many state hospitals were closed in a process called deinstitutionalization. It was generally considered to be unsuccessful as there were no suitable place for ten committed the patients to go. This has led to an increase in the homeless population. Many patients that are seen frequently in a PES would in the past have been committed to a state hospital.

Typical psychiatric emergencies involve suicidal thoughts, psychosis and drug intoxication. These are not specific diagnoses, but patients often fall into one of these categories.

Often patients can stay in an emergency psychiatric facility for up to 24 hours. After which they are several possiblities. Patients may be admitted to an in-patient psychiatric unit. They may be transferred to a medical unit, if have an underlying, non-psychiatric, general medical problem. Patients may be discharged home, with a friend, to an unlocked facility in the community or to a shelter.